Trouble deleting mesh parts from sculpting -From symmetric View
You could remove the vertices in Edit Mode and use Symmetrize function to make identical changes on the other size.
Select the pinching vertices and delete them. Fix the hole that was left behind. Select all a and under Mesh select Symmetrize. In your model x asix is up so you need to use Symmetrize direction +Z to -Z to make the other arm identical.